A wide variety of implantable medical devices (IMDs) that employ electronic circuitry for providing various therapies such as electrical stimulation of body tissue, monitoring a physiologic condition, and/or providing a substance are known in the art. For example, cardiac pacemakers and implantable cardioverter-defibrillators (ICDs) have been developed for maintaining a desired heart rate during episodes of bradycardia or for applying cardioversion or defibrillation therapies to the heart upon detection of serious arrhythmias. Other devices deliver drugs to the brain, muscle and organ tissues, and/or nerves for treatment of a variety of conditions.
Over the past 20 years, the IMDs have evolved from relatively bulky, crude, and short-lived devices to complex, long-lived, and miniaturized IMDs that are steadily being miniaturized with their functionality continuously increasing. For example, numerous improvements have been made in cardioversion/defibrillation leads and electrodes that have enabled the cardioversion/defibrillation energy to be precisely delivered about selected upper and lower heart chambers and thereby dramatically reducing the delivered shock energy required to cardiovert or defibrillate the heart chamber. Moreover, the high voltage output circuitry has been improved in many respects to provide monophasic, biphasic, or multi-phase cardioversion/defibrillation stimulation (shock or pulse) waveforms that are efficacious, sometimes with particular combinations of cardioversion/defibrillation electrodes, in lowering the required shock energy to cardiovert or defibrillate the heart.
The miniaturization of IMDs is driving size and cost reduction of all IMD components including the electronic circuitry components, where it is desirable to reduce the size so that the overall circuitry can be more compact. The IMDs are powered by an internal power source, typically one or more batteries, that serves a variety of functions, including, but not limited to, supplying power to electronic components and circuitry and charging high voltage capacitors that are discharged through medical electrical leads into the heart to regulate heart rhythms. The functional sophistication and complexity of the IMD operating systems powered by the battery have increased over the years.
Despite the advances, battery powered IMDs must be replaced when the battery becomes depleted, and therefore conserving battery power remains important to maintain or prolong the life of the IMD. Therefore, as the dimensions of the IMDs decreases, the electronic circuits of the IMD circuitry are preferred to decrease power consumption in order to maintain or increase longevity.